Solid waste disposal method and apparatus

ABSTRACT

This invention relates to a solid waste disposal apparatus that includes a rotary furnace arranged upstream of a rotary dryer in end-to-end relation to the latter but separated therefrom by a burning chamber and stationary ash removal subassembly interposed therebetween. The raw feed is mixed with a portion of the dried feed from the discharge end of the dryer and introduced into the intake end of the dryer as a moist mixture containing between approximately 40-60 percent water. The remaining dried material is introduced into the furnace. A forced draft burner at the entrance to the furnace is canted in the direction of furnace rotation so as to direct the hot products of combustion spirally along the wall thereof in concurrent flow relation to the moist mixture. Combustion takes place within the upstream end of the furnace inside a separate hollow combustion chamber that cooperates with the furnace wall to define an annulus into which the dryer gas is recycled and mixed with the products of combustion as they leave the aforesaid combustion chamber to reduce the temperature and axial velocity of the latter preparatory to delivering same to the burning chamber and ash removal subassembly complete with exhaust gas system, and dryer inlet therebeyond. The dryer is intricately baffled with a short fall fill that materially increases its efficiency. The ash removal subassembly includes a hopper into which the ashes fall and are sucked out of the top thereof and used to preheat the primary combustion airstream. The exhaust gases are exhausted through a heat recovery system and then scrubbed prior to release to the atmosphere. The invention also encompasses the novel method of treating solid wastes which comprises mixing the raw waste material with a previously dried portion thereof to make up a mixture having between approximately 40 and 60 percent moisture preparatory to drying same, drying the mixture thus produced with a heated gas mixture formed by combining within a mixing and cooling zone in the furnace the gaseous discharge from the dryer with the gaseous products of combustion generated in a combustion zone immediately upstream thereof, separating the solid products of combustion from the heated gas mixture prior to delivering a portion of the latter to the dryer, drawing off a portion of said heated gas mixture and treating it to remove entrained solids and odors prior to exhausting same to the atmosphere.

United States Patent Porter et a1.

SOLID WASTE DISPOSAL METHOD AND APPARATUS [75] Inventors: Stuart M.Porter, Denver; Ervin C. Weimer; Harold W. Shideler, both of Wheatridge,all of Colo.

[73] Assignee: Stearns-Roger Corporation, Glendale, C010.

[22] Filed: April 1, 1971 [21] Appl. No.: 130,224

[52] US. Cl ..110/l4, 110/15 [51] Int. Cl ..F23g 5/06 [58] Field ofSearch ..110/8 R,14,15

[56] References Cited UNITED STATES PATENTS 2,213,667 9/1940 Dundes etal ..1 10/14 1,974,231 9/1934 Bighouse ..l10/14 X 2,148,447 2/1939Dundes et al.... ..110/

2,043,459 6/1936 Windecker ..110/14 2,274,780 3/1942 Duerr et a1...l10/14 Primary Examiner-Kenneth W. Sprague Attorney-Anderson, Spangler& Wymore [5 7] ABSTRACT This invention relates to a solid waste disposalapparatus that includes a rotary furnace arranged upstream of a rotarydryer in end-to-end relation to the latter but separated therefrom by aburning chamber and stationary ash removal subassembly interposedtherebetween. The raw feed is mixed with a portion of the dried feedfrom the discharge end of the dryer and introduced into the intake endof the dryer as a moist mixture containing between approximately -60percent water. The remaining dried material is introduced into thefurnace. A forced draft burner at the entrance to the furnace is cantedin the direction of furnace rotation so as to direct the hot products ofcombustion spirally along the wall thereof in concurrent flow relationto the moist mixture Combustion takes place within the upstream end ofthe furnace inside a separate hollow combustion chamber that cooperateswith the furnace wall to define an annulus into which the dryer gas isrecycled and mixed with the products of combustion as they leave theaforesaid combustion chamber to reduce the temperature and axialvelocity of the latter preparatory to delivering same to the burningchamber and ash removal subassembly complete with exhaust gas system,and dryer inlet therebeyond. The dryer is intricately baffled with ashort fall fill that materially increases its efficiency. The ashremoval subassembly includes a hopper into which the ashes fall and aresucked out of the top thereof and used to preheat the primary combustionairstream. The exhaust gases are exhausted through a heat recoverysystem and then scrubbed prior to release to the atmosphere. Theinvention also encompasses the novel method of treating solid wasteswhich comprises mixing the raw waste material with a previously driedportion thereof to make up a mixture having between approximately 40 andpercent moisture preparatory to dr in same, drying the mixture thusproduced with a ea ed gas mixture formed by combining within a mixingand cooling zone in the furnace the gaseous discharge from the dryerwith the gaseous products of combustion generated in a combustion zoneimmediately upstream thereof, separating the solid products ofcombustion from the heated gas mixture prior to delivering a portion ofthe latter to the dryer, drawing off a portion of said heated gasmixture and treating it to remove entrained solids and odors prior toexhausting same to the atmosphere.

18 Claims, 3 Drawing Figures 68 72 "y s2 sa 48 1 I I8 I a 7 5 52 A I L Iso 62 54 0 2f :1 26F 38 3 i p I am: 1 8i 20F s2 6 22F 2 22F 24 4a 28F30F 22F 22 24 SHEET 2 [IF 2 PATENTEDFEB 13 I975 fmvEN'roRs STUART M. PQRTER ERVIN C. WEIMER HAROLD vW. SHIDELER I ATTORNE48 SOLID WASTE DTSPOSALMETHOD AND APPARATUS The ever-increasing quantity of atmosphericpollutants entering the atmosphere has already reached alarmingproportions and has become a serious health hazard in many of theworld's urban areas. There are many sources responsible for thisdisturbing condition which range, in addition to the vehicle exhaustomissions, all the way from the backyard incinerator to the hugeindustrial complex belching black smoke into the atmosphere.

There is a concerted effort being made at the present time to curb theseabuses of the environment in both the industrial and private sectors ofsociety. Particular attention is being given to the lessening, andhopefully the substantial elimination, of industrial atmosphericpollution in the form of smoke and obnoxious odors. The citiesthemselves are often major offenders as they attempt to dispose of themountains of waste generated daily in the urban community.Unfortunately, this particular problem is a much more involved one thatthat faced by the ordinary industrial plant which, for the most part,knows precisely what it is dumping into the atmosphere and, therefore,has a better chance of controlling it by adopting appropriate remedialmeasures such as changing to a different type of fuel, exerting tightercontrol over a process or preventing the escape of the pollutants insome fashion. The municipal waste disposal facility, on the other hand,has no effective way of controlling the raw material which it must treatand it certainly will have to handle such things as sewage sludge,animal wastes, garbage and refuse of every conceivable type.

It has now been found in accordance with the teaching of the instantinvention that atmospheric pollutants such as fly ash, smoke, odors andobjectionable gases ordinarily generated when an attempt has been madein the past to incinerate solid waste materials can, in large measure,be eliminated by drying before burning. The drying process isaccomplished by first mixing the raw waste with a previously driedportion thereof until the moisture content of the mixture falls withincertain prescribed limits. The resultant mixture is of a spongyconsistency that does not agglomerate readily and clog the feed lifterswithin the rotary drum dryer into which it is fed. The moist mixtureentering the dryer is dried with a precooled mixture of furnace exhaustgases and recycled dryer gases at a temperature of about 1,200F. whichis well below that at which moist materials tend to smoke. The portionof the dried mixture that is not recycled is incinerated in thecombustion zone of a refractory lined rotary furnace after which thesolid products of combustion are separated from the gaseous ones and thelatter are cooled down to around l,200F. preparatory to delivering aportion thereof to the dryer as aforesaid by mixing them with therecycled dryer gases at about 250F. while the remaining portion istreated to remove any remaining solid wastes entrained therein togetherwith any odors before being released to the atmosphere.

It is, therefore, the principal object of the present invention toprovide a novel and improved solid waste disposal apparatus.

A second objective of the invention herein disclosed and claimed' is toprovide an improved method for disposing of solid wastes.

Another object of the invention forming the subject matter hereof is toprovide a waste treatment system wherein the raw wet waste is premixedwith dry wastes to control the moisture content thereof preparatory todrying the mixture with low temperature gases.

Still another objective of the within described invention is theprovision ofa drying and incinerating system for solid waste treatmentwherein the exhaust gases from the dryer are mixed with the gaseousproducts of combustion from the furnace preparatory to recycling sameinto the dryer or releasing to atmosphere.

Further objects are to provide a solid waste disposal facility that isversatile, economical to operate, relatively small, easy to service andrepair, rugged, reliable and efficient.

Other objects will be in part apparent and in part pointed outspecifically hereinafter in connection with the description of thedrawings that follows, and in which:

FIG. 1 is a somewhat schematic side elevation of the solid wastedisposal apparatus of the present invention, portions thereof havingbeen broken away to expose elements otherwise hidden;

FIG. 2 is an end view in highly diagrammatic form illustrating the typeof preferred interior baffling within the dryer; and,

FIG. 3 is a view similar to FIG. 1 but showing a slightly modifiedversion of the apparatus in the form of a flow sheet.

Referring next to the drawings for a detailed description of the presentinvention and, initially, to FIGS. 1 and 3 for this purpose, referencenumeral 10 has been chosen to represent the solid waste disposal systemin its entirety, whereas, numeral 12 is used to similarly denominate thefurnace, number 14 the dryer, and 16 the ash removal subassemblyinterposed between the latter. Since the process starts with the dryingoperation rather than the incineration of the waste, it will'be well tofirst examine dryer l4 and its appurtenances.

This dryer is of the horizontal rotary drum type wherein drum 18 isencircled at longitudinally-spaced points by circumferential rails 20which are, in turn, supported atop trunnions 22 that cradle same forrotational movement. Since the dryer has its axis of rotation inclinedslightly so that the material being dried therein will gravitate slowlytoward the discharge end thereof, trunnions 24 are also needed that liein rolling engagement with the sides of one of the rails 20, all ofwhich is, of course, quite common in the design of a rotary drum dryer.Rotation of the dryer is accomplished by a conventional meshed set ofgears, one of which 26 encircles the drum while the other 28 is mountedon the output shaft of motor 30.

The input to the dryer comprises a moisture controlled mixtureconsisting partly of wet raw feed and partly of unburned recycled dryfeed combined in the proportions necessary to maintain a moisture levelof between approximately 40 and percent water. The raw feed which has inexcess of 60 percent water is delivered to the raw feed intake 32 ofmixing conveyor 34 where it is combined in the proper proportions withthe dried, but yet unburned, feed entering dry feed intake 36 of thelatter. Both intakes 32 and 36 are, of course, positioned adjacent oneanother at the upstream end of the mixing conveyor which can take anyone of several different conventional forms, the splitflight screw typehaving been found quite adequate for the purpose. A gravity chute 38 atthe discharge end of the mixing conveyor directs the moist mixture intothe intake end of dryer 14.

With brief reference to FIG. 2, it will be seen that the dryerpreferably has the interior wall thereof provided with feed lifters 40of conventional design that tumble the mixture and generally contributeto improved drying efficiency. More important than the lifters, however,is the fact that the interior of the dryer is preferably filled withcross-type short fall fill 42 that keeps the moist feed mixture almostconstantly in contact with a hot surface that conducts heat directlythereto rather than relying on air drying as the material falls freewithin the interior of the drum, the latter being much less efficient.Also, the fill 42 leaves very little open space for free fall of thematerial hence the designation short fall fill is used previously.

Now, by controlling the moisture content of the ordinary sticky typewaste material entering the dryer to between approximately 40-60 percentwater, it has a spongy consistency that will not stick to or otherwiseagglomerate on the feed lifters 40 or the cross-type fills 42 thusassuring a proper drying action and an almost completely dehydratedproduct which leaves the dryer at preferably a temperature approaching200F. so that most of the bacteria will have been killed. A wettermixture of the stick product (one containing in excess of 60 percentwater) tends to cake and stick to the hot conduction surfaces resultingin a good deal of surface drying with little of the internal moisturebeing removed due to inadequate mixing.

Again with reference to FIGS; 1 and 3, the dehydrated mixture thatfinally gravitates to the discharge end of the dryer leaves same ataround 200F. and strikes a baffle plate 44 (broken lines in FIG. 1)projecting outwardly and downwardly into stationary hopper 46 whereseparation of the gaseous and solid constituents first takes place. Asthe dry solids contact the inclined baffle plate, they are directeddownwardly I into the bottom of the hopper 46 when they drop into theintake end of dry feed conveyor 48; whereas, the gaseous constituentsincluding undoubtedly, some dust and other suspended solids, is suckedout of the top of the hopper 46 by suction fan 50 which delivers it intothe intake end of recycle gas duct 52 at a temperature of around 250F.Now, dry feed conveyor- 48 extends from the bottom of hopper 46 at thedischarge end of the dryer 14 up to the intake end of furnace 12 wheregravity chute 54 delivers the dry feed directly into the combustion zone56 thereof. Branch 58 in the dry feed conveyor upstream of the dischargeend thereof shunts a portion of the dry feed off into dry feed intake 36for recycling with the wet feed in the form of the moist mixtureentering the dryer or dehydrator 14. A valve 60 interposed between thedry feed conveyor 48 and the mixing conveyor 34 is used to control theproportion of the dry feed that is recycled to produce the moist mixturehaving the desired water content.

In the particular form shown, dry feed conveyor 48 is of screw-type aswas the case with the mixing conveyor 34 already described. In the dryfeed conveyor, on the other hand, asolid helicoidal auger flighting 62would be preferred to the split or ribbon-type helicoidal flighting 64ordinarily employed in screw-type mixing conveyors. Here again,conveyors for the dry feed of other than the screw-type can,undoubtedly, be used, but, from the standpoints of both economics andefficiency in material movement, there would seem to be little reasonfor using any other type of conveyor.

Continuing on with an examination of FIGS. 1 and 3,

the furnace 12 will be seen to be of the refractory lined rotary typehaving its rails 20F cradled in trunnions 22F and 24F while its drum 18Fis driven by motor 30F and meshed gears 26F and 28F in much the samemanner as the dryer already described. As shown, the furnace 12 of theFIG. 1 apparatus has its axis of rotation tilted downwardly to asomewhat greater degree than its companion dryer 14 in order to maintainabout the same thru-put while permitting the furnace drum to be turnedmore slowly for the purpose of insuring complete combustion.

The burner 66 is located at the entrance to the combustion zone 56 inthe intake end of the furnace. Preheated combustion air enters thefurnace at the same point through combustion air duct 68 through whichthe air is forced by means of fan 70 located at its intake end. lnthe'preferred embodiment of the invention, this combustion air ispreheated by passing it in heat exchange relation over heat exchanger72located in the stack 74 that carries the hot exhaust gases.

Burner 66 can be any one of several commercially available types thatburn gas, oil, coal, sander dust, hogged fuels or any other suitablefuel. About the only feature of burner 66 deserving of specific mentionis its orientation relative to the furnace. The burner is preferablyoriented such that the flame issuing therefrom will circulate helicallyalong the inside wall 68 of the combustion zone in concurrent flowrelation to the dry feed progressing therethrough as indicated by thearrows 76 in FIG. 3. This swirling flame pattern inside the combustionzone 56 removes any residual moisture left in the dry feed from thedryer and incinerates it until all that is left as residue are the ashesand gaseous products of combustion. 1

Now, in the furnace of FIG. 1, the combustion zone 56 is defined by atubular member 78 located within the intake end of the drum 18F so as toleave an annular space 80 therebetween. In the particular form shown,number 78 is cylindrical and coaxial with the drum although terminatingwell short of the discharge end of the latter. The dry feed inlet chute54 discharges the feed into about the center of the combustion zonedefined by member 78 and the burner 66 is offset toward the bottom ofthelatter.

The significance of annular space 80 surrounding the combustion zone isthat a circular manifold 82 is mounted in stationary position at theentrance to the furnace connected to receive the gases discharged fromthe dryer through duct 52 and directed same into this annulus. Thus,while the dry solid wastes are being incinerated at a temperature ofaround 2,500F. within the combustion zone 56, the considerable coolergases from the dryer (250 F.) are moving along the outside thereofwithin annulus 80. v

The waste material is completely burned withincombustion zone 56 whereit is in intimate contact with the burner flame. The ashes leaving theend of tubular member 78 drop directly down into the bottom of thefurnace while the gaseous products of combustion combine with the coolerdryer gases to form a mixture for drying purposes having a temperatureof around 1,200F. that will dehydrate the moist waste material enteringthe dryer without causing it to smoke. Thus, despite the fact that thetemperature within the combustion zone is quite high (2,500F. or so),the gases entering the dryer have been cooleddown considerably to around1,200F. thereby eliminating the intermediate temperature range ofbetween approximately 1,400F. and 1,800F. where wet materials tend tosmoke the worst.

Before providing further with a description of the gaseous and solidproduct separation and discharge that takes place at the interfacebetween the adjacent ends of the furnace and dryer, it would beadvisable to examine briefly the modified furnace 12 as of FIG. 3.Combustion zone 56 remains much the same except that it is not housedwithin a tubular member 78 not is it encircled by cold gas annulus 80 aswas the case with the FIG. 1 configuration. Instead, drum 18PM isenlarged at the interface between the combustion zone 56 and the coolingzone 84 adjacent thereto to define a shoulder 86 facing back upstreamagainst which abuts the stationary collar 82M that defines the cool, airmanifold. Suitable openings (not shown) in the manifold and rotatingshoulder of the drum register with one another upon relative rotationalmovement therebetween and mix the cool dryer air with the products ofcombustion leaving the combustion zone. Thus, the mixing of thecombustion products and dryer air takes place immediately at the end ofthe combustion zone rather than having them move along in the furnaceside-by-side but separated physically from one another prior to beingcombined at much the same point.

Returning once again to FIGS. 1 and 3, both systems include a separationzone 88 interconnecting the furnace l2 and the dryer 14 within which thesolid products of combustion are separated from the gaseousconstituents. Each includes a stationary coupling member 90, theupstream end of which is connected to the discharge end of the furnaceand is adapted to receive both the solid and gaseous products therefromwhile the downstream end is connected to deliver the pre-cooled productsof combustion into the dryer entrance. Moist feed mixture chute 38enters the dryer "through this coupling 90 in both configurations. Also,

both units have the exhaust gas stack 74 connected into the top ofcoupling 90 and a solid waste receiver 92 in the bottom thereof. Theashes entering the solidwaste receiver 92 are disposed of elsewhere inthe usual manner while the gaseous constituents are divided into twoportions, one passing up the stack 74 for further processing in a mannerto be explained presently while the rest are recycled back into themouth of the dryer. Up to approximately 50 percent of the gas leavingthe discharge end of the dryer can be recycled while the remainderpasses out through the stack. In the particular form of the coupling 90Millustrated in FIG. 3, it includes a dryer gas by-pass 92 at-the throator mouth of the dryer connected to take some gas from dryer gas duct 52before it reaches the entrance to the furnace. Dampers 94 in duct 52 andby-pass 92 downstream of the intersection therebetween enable therelative proportions of the dryer gas directly recycled and passing onto the furnace for cooling purposes to be varied.

Finally, the exhaust gases leaving the system through stack 74 arepreferably given further treatment to eliminate entrained dust and odorsbefore being discharged to the atmosphere. Fan 96 sucks the exhaustgases up the stack where, in FIG. 3, they pass through a cycloneseparator 98 which drops out any remaining suspended solids. The exhaustgases leaving the cyclone stack can, if necessary, be fired inafterburner 100 to remove any residual odors or smoke as shownschematically in FIG. 3.

FIG. 1 shows the use of a scrubber 102 in the stack to knock downentrained solids in place of the cyclone 98 shown in FIG. 3. Such ascrubber can use either water or chemical scrubbers depending upon themake up of the exhaust gases. Here again, an afterburner can be added ifnecessary. A single 8 foot diameter drum dryer will handle approximately300 tons/day of raw waste material when incorporated into a wastetreatment facility of the type forming the subject matter hereof. Otherdryer drums are available in diameters from 4 to 12 feet with comparablecapacities.

What is claimed is:

l. The solid waste disposal apparatus which comprises: ahorizontally-disposed rotating drum furnace having a combustion zoneadjacent the intake end thereof and a cooling zone adjacent its outletend; a horizontally-disposed rotating drum dryer positioned with itsinlet end in axially spaced relation to the outlet end of the furnace;stationary hopper means positioned to receive the dry solids and dryergases discharged from the dryer; dry solids conveyor means connected toreceive the dry solids discharged into the hopper from the dryer anddeliver same into the combustion zone of the furnace through the intakeend thereof; forced draft gas conduit means connected to receive thedryer gases discharged into the hopper from the dryer and introduce sameintothe cooling zone thereof in position to mix with the gaseousproducts of combustion issuing from the combustion zone; burner meansmounted in the inlet end of the furnace in position to direct a flameinto the combustion zone thereof; a source of combustion air connectedinto the burner; raw feed mixing conveyor means connectable to a sourceof wet solid wastes and connected to deliver same into the dryer inlet;dryer feed blending means comprising a flow controlled conduit connectedbetween the raw feed conveyor and dry solids conveyor means adapted torecycle a portion of the latter to be mixed with the raw feed to form amoisture controlled mixture; stationary coupling means defining apassage interconnecting the discharge end of the furnace and the inletend of the dryer adapted to pass the precooled mixture of the recycleddryer gases and products of combustion into the latter; ash removalmeans corinected into the bottom of the coupling means adapted to removethe incinerated solid wastes generated in the combustion zone of thefurnace therefrom; and, an exhaust gas stack connected into saidcoupling positioned and adapted to remove a portion of the precooledmixture entering the dryer.

2. The solid waste disposal apparatus as set forth in claim 1 in which:a heat exchanger is located downstream of the stack connected to receivethe exhaust gases therefrom; and, in which the source of combustion aircomprises a forced draft air duct connected to pass the combustion airin heat exchange relation to said heat exchanger.

3. The solid waste disposal apparatus as set forth in claim 1 in which:dust removal means is located downstream of the stack connected toreceive the exhaust gases therefrom and remove any entrained solidsprior to releasing same to the atmosphere.

4. The solid waste disposal apparatus as set forth in claim 1 in which:by-pass conduit means is connected between the forced draft conduitmeans and the dryer inlet operative to recycle a portion of the dryergas without circulating same through the furnace.

5. The solid waste disposal apparatus as set forth in claim 1 in which:the furnace includes interior wall means adjacent the intake endcooperating with the adjacent furnace wall to define an annular air ductseparate from the combustion zone but merging therewith at the entranceto the cooling zone; and, in which a stationary manifold communicatesthe interior of said annular furnace duct and is connected to receivedryer air from the forced draft gas conduit means.

6. The solid waste disposal apparatus as set forth in claim 1 in which:the furnace is provided with dryer air intake ports opening onto theexterior thereof at the interface between the combustion and coolingzones; and, in which a stationary manifold-forming collar encircles saiddryer air intake ports and is connected to the forced draft gas conduitmeans for delivering dryer air to the latter.

7. The solid waste disposal apparatus as set forth in claim 1 in which:the burner means is canted to direct the flame issuing therefrom throughthe combustion zone along a helicoidal path in concurrent flow relationto the dry solid wastes being incinerated therein.

' 8. The solid waste disposal apparatus as set forth in claim 1 inwhich: feed lifters are provided on the inside periphery of the dryerand the interior thereof contains baffling with an x-shaped crosssection that defines a short fall till.

9. The solid waste disposal apparatus as set forth in claim 1 in which:an afterburner is located downstream of the stack connected to receivethe exhaust gases therefrom and reincinerate any entrained solids lefttherein.

10. The solid waste disposal apparatus as set forth in claim 3 in which:the dust removal apparatus comprises a cyclone.

11. The solid waste disposal apparatus as set forth in claim 3 in which:the dust removal apparatus comprises a scrubber.

12. The solid waste disposal apparatus as set forth in claim 11 inwhich: a flow control damper is connected into the by-pass conduit meansfor regulating the volume of dryer gas recycled directly to the dryer.

13. The method for drying and incinerating wet solid waste materialswhich comprises: dehydrating a moist solid waste mixture having amoisture content of between approximately 40 percent and approximately60 percent by-passing a warm gas mixture at a temperature ofapproximately l,200F. in heat exchange relation thereto; recycling aportion of the dehydrated mixture with raw wet feed to produce the moistmixture ure content; burning the having the required mols remainder ofthe dehydrated mixture; cooling the hot dry gaseous products ofcombustion with a recycled portion of the wet gaseous products ofdehydration to produce said warm gas mixture preparatory to dehydratingthe moist solid waste mixture therewith; separating the solid productsof combustion from the warm gas mixture; and exhausting a portion of thewarm gas mixture while using the remainder thereof containing up toapproximately 50 percent recycled gaseous products of dehydration fordehydrating the moist solid waste mixture.

14. The method as set forth in claim 13 which includes the step of:scrubbing the warm exhaust gas mixture to remove suspended solidstherefrom.

15. The method as set forth in claim 13 which includes the step of:reburnin g the warm exhaust gas mixture to incinerate solids suspendedtherein.

16. The method as set forth in claim 13 which includes the step of:centrifugally treating the warm exhaust gas mixture to remove suspendedsolids therefrom.

17. The method as set forth in claim 13 which includes the step of:directly recycling a portion of the cool wet gaseous products ofdehydration by mixing same with the portion of the warm gas mixture usedfor dehydration purposes after the latter has been mixed.

18. The method as set forth in claim 13 which includes the step of:rebuming'the warm exhaust gas mixtureto eliminate odors therein.

1. The solid waste disposal apparatus which comprises: ahorizontally-disposed rotating drum furnace having a combustion zoneadjacent the intake end thereof and a cooling zone adjacent its outletend; a horizontally-disposed rotating drum dryer positioned with itsinlet end in axially spaced relation to the outlet end of the furnace;stationary hopper means positioned to receive the dry solids and dryergases discharged from the dryer; dry solids conveyor means connected toreceive the dry solids discharged into the hopper from the dryer anddeliver same into the combustion zone of the furnace through the intakeend thereof; forced draft gas conduit means connected to receive thedryer gases discharged into the hopper from the dryer and introduce sameinto the cooling zone thereof in position to mix with the gaseousproducts of combustion issuing from the combustion zone; burner meansmounted in the inlet end of the furnace in position to direct a flameinto the combustion zone thereof; a source of combustion air connectedinto the burner; raw feed mixing conveyor means connectable to a sourceof wet solid wastes and connected to deliver same into the dryer inlet;dryer feed blending means comprising a flow controlled conduit connectedbetween the raw feed conveyor and dry solids conveyor means adapted torecycle a portion of the latter to be mixed with the raw feed to form amoisture controlled mixture; stationary coupling means defining apassage interconnecting the discharge end of the furnace and the inletend of the dryer adapted to pass the precooled mixture of the recycleddryer gases and products of combustion into the latter; ash removalmeans connected into the bottom of the coupling means adapted to removethe incinerated solid wastes generated in the combustion zone of thefurnace therefrom; and, an exhaust gas stack connected into saidcoupling positioned and adapted to remove a portion of the precooledmixture entering the dryer.
 1. The solid waste disposal apparatus whichcomprises: a horizontally-disposed rotating drum furnace having acombustion zone adjacent the intake end thereof and a cooling zoneadjacent its outlet end; a horizontally-disposed rotating drum dryerpositioned with its inlet end in axially spaced relation to the outletend of the furnace; stationary hopper means positioned to receive thedry solids and dryer gases discharged from the dryer; dry solidsconveyor means connected to receive the dry solids discharged into thehopper from the dryer and deliver same into the combustion zone of thefurnace through the intake end thereof; forced draft gas conduit meansconnected to receive the dryer gases discharged into the hopper from thedryer and introduce same into the cooling zone thereof in position tomix with the gaseous products of combustion issuing from the combustionzone; burner means mounted in the inlet end of the furnace in positionto direct a flame into the combustion zone thereof; a source ofcombustion air connected into the burner; raw feed mixing conveyor meansconnectable to a source of wet solid wastes and connected to deliversame into the dryer inlet; dryer feed blending means comprising a flowcontrolled conduit connected between the raw feed conveyor and drysolids conveyor means adapted to recycle a portion of the latter to bemixed with the raw feed to form a moisture controlled mixture;stationary coupling means defining a passage interconnecting thedischarge end of the furnace and the inlet end of the dryer adapted topass the precooled mixture of the recycled dryer gases and products ofcombustion into the latter; ash removal means connected into the bottomof the coupling means adapted to remove the incinerated solid wastesgenerated in the combustion zone of the furnace therefrom; and, anexhaust gas stack connected into said coupling positioned and adapted toremove a portion of the precooled mixture entering the dryer.
 2. Thesolid waste disposal apparatus as set forth in claim 1 in which: a heatexchanger is located downstream of the stack connected to receive theexhaust gases therefrom; and, in which the source of combustion aircomprises a forced draft air duct connected to pass the combustion airin heat exchange relation to said heat exchanger.
 3. The solid wastedisposal apparatus as set forth in claim 1 in which: dust removal meansis located downstream of the stack connected to receive the exhaustgases therefrom and remove any entrained solids prior to releasing sameto the atmosphere.
 4. The solid waste disposal apparatus as set forth inclaim 1 in which: by-pass conduit means is connected between the forcEddraft conduit means and the dryer inlet operative to recycle a portionof the dryer gas without circulating same through the furnace.
 5. Thesolid waste disposal apparatus as set forth in claim 1 in which: thefurnace includes interior wall means adjacent the intake end cooperatingwith the adjacent furnace wall to define an annular air duct separatefrom the combustion zone but merging therewith at the entrance to thecooling zone; and, in which a stationary manifold communicates theinterior of said annular furnace duct and is connected to receive dryerair from the forced draft gas conduit means.
 6. The solid waste disposalapparatus as set forth in claim 1 in which: the furnace is provided withdryer air intake ports opening onto the exterior thereof at theinterface between the combustion and cooling zones; and, in which astationary manifold-forming collar encircles said dryer air intake portsand is connected to the forced draft gas conduit means for deliveringdryer air to the latter.
 7. The solid waste disposal apparatus as setforth in claim 1 in which: the burner means is canted to direct theflame issuing therefrom through the combustion zone along a helicoidalpath in concurrent flow relation to the dry solid wastes beingincinerated therein.
 8. The solid waste disposal apparatus as set forthin claim 1 in which: feed lifters are provided on the inside peripheryof the dryer and the interior thereof contains baffling with an x-shapedcross section that defines a short fall fill.
 9. The solid wastedisposal apparatus as set forth in claim 1 in which: an afterburner islocated downstream of the stack connected to receive the exhaust gasestherefrom and reincinerate any entrained solids left therein.
 10. Thesolid waste disposal apparatus as set forth in claim 3 in which: thedust removal apparatus comprises a cyclone.
 11. The solid waste disposalapparatus as set forth in claim 3 in which: the dust removal apparatuscomprises a scrubber.
 12. The solid waste disposal apparatus as setforth in claim 11 in which: a flow control damper is connected into theby-pass conduit means for regulating the volume of dryer gas recycleddirectly to the dryer.
 13. The method for drying and incinerating wetsolid waste materials which comprises: dehydrating a moist solid wastemixture having a moisture content of between approximately 40 percentand approximately 60 percent by-passing a warm gas mixture at atemperature of approximately 1,200*F. in heat exchange relation thereto;recycling a portion of the dehydrated mixture with raw wet feed toproduce the moist mixture having the required moisture content; burningthe remainder of the dehydrated mixture; cooling the hot dry gaseousproducts of combustion with a recycled portion of the wet gaseousproducts of dehydration to produce said warm gas mixture preparatory todehydrating the moist solid waste mixture therewith; separating thesolid products of combustion from the warm gas mixture; and exhausting aportion of the warm gas mixture while using the remainder thereofcontaining up to approximately 50 percent recycled gaseous products ofdehydration for dehydrating the moist solid waste mixture.
 14. Themethod as set forth in claim 13 which includes the step of: scrubbingthe warm exhaust gas mixture to remove suspended solids therefrom. 15.The method as set forth in claim 13 which includes the step of:reburning the warm exhaust gas mixture to incinerate solids suspendedtherein.
 16. The method as set forth in claim 13 which includes the stepof: centrifugally treating the warm exhaust gas mixture to removesuspended solids therefrom.
 17. The method as set forth in claim 13which includes the step of: directly recycling a portion of the cool wetgaseous products of dehydration by mixing same with the portion of thewarm gas mixture used for dehydration purposes after the latter has beenmixed.